I would just like to point out first i'm level 87 and i can say from experience it works for me. i currently have 3.8 Million dollars.

First your gonna going to need AT LEAST $300,000 to buy oil frackers which usually get you$45,000 for 50oil, And each fracker makes about 30 every ten minutes. Which is 180oil every ten minutes if you have all frackers. So in a hour you will make about $1,000,000 to $1,475,000.

To Get This Money i recommend (IN ORDER)3. If you are really noobish kill zombies until you get enough money.2. Printers, max printers all upgraded would be just enough to get you 100k every hour1. Meth is probably the second best way to get money other than oil.

I recommend basing near a oil NPC, and keeping your base heavily armed/Guarded for maximum security.Base with 2+ people so when you go out to sell other people can guard the base, and make sure you have a way of communication (Steam,Skype.) so he can tell you if your being raided.